So the other day I went into my car and sat down, started it up, and turned on the ventilation. It was set at 16 Celsius (or 60.8 F) but there was this AWFUL smelling warm-air coming out of the vents! I was gagging inside my car!!! I immediately hit the Frost-button to get some cold air and then after maybe a minute it was gone and clear.

But the thing is, when I put the heater to 28 degrees Celsius (82.4 F) and it couldn't even stand sitting in the car. This hot-garbage smelling air comes rushing out of the vents. WTF is this?

Should I get this checked out? It only happens when I just turn on the vents, no AC or Heater. I'm 100% sure it's not from the outside because I rolled down all windows to clear out the car.

Usually it's mold buildup because condensation from the A/C isn't able to drain adequately(sp?). You live in a very cool and wet climate, and to be honest I can't see how you would every drive the car w/out the A/C running. The smell will disappear after you've run the heat + A/C for awhile..

I'm a little bit confused here. If this is mold build-up in my vents, shouldn't that be checked on? Should I take it to the dealer or is there some DIY method (like cranking the heater at max and letting it run for like 20 mins LOL)?

It's only been happening since the last 2-3 days. Before then I could turn it on without any issue or smell...

What do you guys mean by air-recirculation button, would that make it musty?

It's a known issue, and although there seems to be some temporary fixes to it, there really isn't a permanent solution. It was the same with my E46 as well.

The most popular way to prevent it is to run the climate control with the A/C off for a few minutes before shutting the car off. Other people have suggested spraying disinfectant into the intake vent, but I've never tried it.

I take my Ionizer set it on passenger floor, put it on high and set the a/c to recirc with the temp set really low for maximum blow for 5 minutes, works great and I beleive the high level of ionized air kills any bacteria as well. You do not want to be inside the car while doing this especially if you have a high output ionizer.

It's a known issue, and although there seems to be some temporary fixes to it, there really isn't a permanent solution. It was the same with my E46 as well.

The most popular way to prevent it is to run the climate control with the A/C off for a few minutes before shutting the car off. Other people have suggested spraying disinfectant into the intake vent, but I've never tried it.

This is the best way to resolve the immediate problem.

What happens is that while running the AC, moisture condenses out onto the cooling coil. (It's suppose to do that, it's how the air gets de-humidified). But if the AC is working on humid air and the coil is wet then you shut down the car, some of that moisture currently on the coil will not go down the drain and will just stay there.
Now let it sit in the heat for a while and some mold can grow. Next time you turn on the fan, A/C or heating whatever, you get that moldy gym-sock smell.

The fast way to get rid of the smell is just to kick the fan up high. I don't remember if the air from the heating core goes through the cooling coil, or if it's the other way around. If the heater is upstream, then turning on the heater would also help dry out the residual moisture.

This is a common problem down here in the south, for any kind of car. The only easy way to prevent it is to shut down the compressor (but leave the fan running), for the last 5 minutes or so you are in the car. That way the AC coil gets dried off.

I did read a DIY a while ago, about someone who had this problem often enough that he found out that the AC coil drain pan could be reached by the hump by the drivers right knee. He drilled a small hole into the drain pan and put a colored cover on the hole. When he got the smell, he unplugged it and had some deodorizer / mold-killer with a long plastic tub he could put in the hole and spray the core.

What happens is that while running the AC, moisture condenses out onto the cooling coil. (It's suppose to do that, it's how the air gets de-humidified). But if the AC is working on humid air and the coil is wet then you shut down the car, some of that moisture currently on the coil will not go down the drain and will just stay there.
Now let it sit in the heat for a while and some mold can grow. Next time you turn on the fan, A/C or heating whatever, you get that moldy gym-sock smell.

The fast way to get rid of the smell is just to kick the fan up high. I don't remember if the air from the heating core goes through the cooling coil, or if it's the other way around. If the heater is upstream, then turning on the heater would also help dry out the residual moisture.

This is a common problem down here in the south, for any kind of car. The only easy way to prevent it is to shut down the compressor (but leave the fan running), for the last 5 minutes or so you are in the car. That way the AC coil gets dried off.

I did read a DIY a while ago, about someone who had this problem often enough that he found out that the AC coil drain pan could be reached by the hump by the drivers right knee. He drilled a small hole into the drain pan and put a colored cover on the hole. When he got the smell, he unplugged it and had some deodorizer / mold-killer with a long plastic tub he could put in the hole and spray the core.

I don't think I want to drill a hole anywhere in my car...
But that was very informative and thank you! Now, when you say to turn the fan on "high", do you mean temperature-wise or just speed?

Before you start driving, turn on your car, and turn the heater on all the way at the highest temperature with all the doors and windows closed. Then wait a few minutes and get into the car and turn the AC on. He said the high temperature helps in reducing the mold build-up. It won't completely get rid of the mold, but it helps a lot.

It could be an annoying procedure but you don't have to do it everyday, just once a week or something until the smell is improved. I've done it to my car and I've seen a huge improvement after a couple of weeks of doing it. Give it a try

Before you start driving, turn on your car, and turn the heater on all the way at the highest temperature with all the doors and windows closed. Then wait a few minutes and get into the car and turn the AC on. He said the high temperature helps in reducing the mold build-up. It won't completely get rid of the mold, but it helps a lot.

It could be an annoying procedure but you don't have to do it everyday, just once a week or something until the smell is improved. I've done it to my car and I've seen a huge improvement after a couple of weeks of doing it. Give it a try

Had this problem with one on my vehicles - Like he said, crank the heat to get rid of the mold build up.

i have problem with my e90 too. it appears that i dont get the smell but i get something like small white particles. i suspect it is due to taking my car for someone to fix and paint the door that someone had smashed and probably was painting with the windows open or something. whenever i press auto and the fan kicks in on max (due to outside temperature being around 35 celsius) i get those particles in my eyes and the car looks like a barn after a few seconds. small white particles in millions. the car needs a cleaning every day. i removed the pollen filter from within the engine bay and blew some air with the air compressor. you cant imagine what was happening. trillions of small white particles were flying all over the upholstery. it became white instead of black. i cleaned everything with a vacuum cleaner and the next day the same thing happened. it's very annoying. please also note that this things start flying as soon as i switch the heater on. after a few seconds they disappear. it doesnt matter whether hot or cold they just come out depending on the fan speed. any ideas where the blower motor is located? also the evaporator? i want to see if they are clean. any ideas of what is going on guys? anyone knows how to clean the vents inside?

I had the same issue few weeks ago after i had my AC gas filled up by dealer. The smell is 'unbearable' for few seconds after AC turned on. But now, i noticed the smell is fading off as time passes by. Smell is still there but so much have improved. Hope it will 'go away' totally in a few more days.